In the constructed environment, it's seems that Voice of All is this best creature that Planeshift has to offer. It just stands up to so much. Hello, mister Blastoderm. What's that, you are attacking? Nah, you just stand there. Mister FTK? Why are you trying to shoot me? You know that you'll just miss!

I voted for Voice of All. There's few creatures in Magic who can change or chose their protection. Being invunerable to an entire color is great, the card singlehandedly discourages monocolor decks. Plus the name is just cool

After that, probably the Flametongue Kavu, but his effectiveness is really weakened playing against white. Which has the Voice of All as well as Acolytes.

Thunderscape Battlemage is a close second to Thornscape Battlemage for me. All creatures that get killed by FTK can be killed by Thornscape, and Thornscape kills Orbs, Webs, Millstones, Bridges and Idols. Tough to say that this is better than killing Opposition, Story Circle, Teferi's Moat, Fires or Burst in all cases, but it is a little less situational. So here goes:

Phyrexian ScutaPros:
Can be a 5/5 for 4
Can be a 3/3 if you don't wanna pay the life
Beefy-phat for blackCons:
Costs you 3 life to grow him
Bereft of any other powers
Bounce is not your friend
You still pay 3 life if your opponent counters

Flametongue KavuPros:
Deals 4 when he comes in
Lightning Blast's big brother
Merely uncommon
Big in frontCons:
Can be forced to hit himself
Small backside

Meddling MagePros:
Combo-stopper
Warm body
In-flavor for W/U controlCons:
A 2/2 is easy to kill
Only handles one card
In Type 2, what combos?

Shivan WurmPros:
Absolutely MASSIVE
Tramples
Did I mention he only costs 5 mana?
Works great in Fires, an established archetypeCons:
Gotta bounce something when he comes in
Still vulnerable to tapping and/or Dark Banishing stuff

So it looks like it's down to Shivan Wurm vs. FTK...both very good choices. Amusingly enough, they're good friends. Play FTK for a 4-point splat, play the Wurm, and replay FTK for another splat.